Tobacco smoke filter



Feb. 1, 1966 J. A. ORSINO ETAL 3,232,294

TOBACCO SMOKE FILTER Filed March 5. 1962 Fused Casing Filter- /TobaccoHollow Pori'ion of Polymer Tubule Polymer Tubule with porous WallsINVENTORS Joseph A. Orsino Edgar H. Herrmonn Charles E. Mandel BYWZ a.

ATTORN EY United States Patent Ofiice 3,232,294 Patented Feb. 1, 19663,232,294 TOBACCO SMOKE FILTER Joseph A. Orsino, Mountain Lakes, N.J.,Edgar H. Hermann, Brooklyn, N.Y., and Charles E. Mandel, Freehold, N.J.,assiguors to National Lead Company, New York, N.Y., a corporation of Newlersey Filed Mar. 5, 1962, Ser. No. 177,173 13 Claims. (Cl. ISL-) Thisinvention relates to a filter and, more particularly, to a filter forpurifying fluids such as tobacco smoke.

While the device of this invention is susceptible of a wide variety offiltering applications, as will be readily apparent to those skilled inthe art, it will be described principally with reference to itsapplication to a cigarette filter, because that particular use isparticularly illustrative of the nature and of the utility of thedevice.

The construction of cigarette filters and the selection of filtermaterials therefore has been subject to a considerable amount of study.In general, using conventional filter materials, the construction ofsuch filters has necessarily been a compromise among several mutuallyantagonistic properties. Thus an ideal filter should remove a largeproportion of the tars and nicotine naturally occurring in tobaccosmoke. On the other hand, filters that are effective in this respecttend to be dense and in use, become progressively resistant to thepassage of gases therethrough, resulting in a cigarette that can bepulled only with difiiculty. Also, filters that are effective to removea high percentage of tar and nicotine also tend to be effective inremoving other components of the smoke-bearing vapor stream,particularly by absorption or adsorption of water vapor. This, in turn,makes the smoke dry and harsh, adversely affecting the flavor of thesmoke so that the more efiective filters are unacceptable to theconsumer. Filter effectiveness is, therefore, sacrificed in order tomake a cigarette of acceptable smoking qualities.

An object of this invention is to provide an improved tobacco smokefilter. Another object is to provide a filter medium having lowresistance to the passage of vapors. Still another object is to providea filtration medium for vapor and gas streams which results in a minimumof moisture loss from the filtered gases. Other objects and advantageswill become apparent from the following more complete description andclaims and attached drawing diagrammatically illustrating on an enlargedscale the invention and in which:

FIG. 1 is a longitudinal view of a filter of the instant invention, thecasing of the filter consisting of a surface area of a mass of hollowand porous polymer tubules which have been fused to seal the pores inaccordance with one embodiment of the invention;

FIG. 2 is a partially sectional, longitudinal view of a cigarettecontaining a filter of the instant invention. The casing of the filterand the tobacco portion of the cigarette are enclosed in a cigarettepaper casing in accordance with a further embodiment of the invention;

FIG. 3 is a longitudinal sectional view of a cigarette holder containingand encasing a filter of the instant invention in accordance withanother embodiment of the invention; and

FIG. 4 is an enlarged view of that portion of the filter in the areascircularly enclosed with the dashed lines of FIGS. 1, 2 and 3, andshowing, diagrammatically, hollow polymer tubules having porous walls inaccordance with the instant invention.

Broadly, this invention contemplates a novel filter suitable for thepurification of tobacco smoke or the like, said filter being composed ofa self-supporting micro-porous mass of hollow tubules of a polymer of amonomer selected from the group consisting of aliphatic l-olefins havingless than 6 carbon atoms, said tubules being fused together at theirpoints of contact.

This invention also contemplates a filtering medium for purifyingtobacco smoke which comprises a self-sustaining micro-porous massconsisting essentially of minute, porous tubules of a polymer of amonomer selected from the group consisting of aliphatic l-olefins havingless than 6 carbon atoms, said tubules being fused together at theirpoints of contact.

This invention further contemplates a filter tip cigarette comprising ahousing open at its opposite ends, tobacco in one end of said housingand a filter in the opposite end of said housing, said filter comprisinga mass of hollow tubules of a polymer, said tubules being joinedtogether at their points of contact to form, intermediate said points ofcontact, tortuous paths for the passage of tobacco smoke axially of saidhousing, said hollow tubules having porous walls, the pores in saidWalls connecting the interiors of said tubules with said tortuous paths,said housing adjacent said compacted mass being substantially imperviousto air.

Methods for making porous tubes of poiyolefins by encasing individualcellulosic fibers in polyolefin to form a tube or sleeve aroundindividual fibers and subsequently leaching to remove the cellulosefiber, are more fully described and claimed in copending applicationSerial No. 852,844, filed November 13, 1959, now Patent 3,121,698.

In accordance with the teaching of the above mentioned copendingapplication, fibers or filaments of cellulosic material are encased intubes, sleeves or shells of polyolefin plastic polymerized in situ,preferably by the use of what is known as an organornetallic-transitionmetal catalyst system. The components of such a catalyst system, as willbe understood by those skilled in the polymer art, react when mixedtogether to produce a substance or substances highly active as apolymerization initiator for the low molecular weight aliphaticl-olefins.

Any of the aliphatic l-olefins having less than 6 carbon atoms may beemployed in the manufacture of filters according to the presentinvention. These include the simplest l-olefins such as ethylene,propylene, butene-l and the like and also di-olefins such asbutadiene-1,3 and isoprene. These l-olefins may be used in the form ofhomopolymers, or mixtures of them may be polymerized together to formvarious copolymers. In addition, other compounds which are known tocopoiymerize with these l-olefins to form useful products, may beemployed in combination therewith.

For purposes of the instant invention we prefer to use ethylene orpropylene which have the outstanding advantages of being gases atordinary temperatures, of being relatively inexpensive and available inlarge quantities, and of producing polymers of high molecular weighthaving very desirable properties for filtration purposes.

As disclosed in the aforesaid application, it is important to treat thecellulosic material with one of the components of the catalyst systembefore the components have been mixed together long enough to completetheir reaction with each other. Some reaction appears to take placebetween this catalyst component and the cellulosic material. The exactnature of this reaction is not known but it is thought to involve eitherthe active hydroxyl groups, or the other type linkages of the cellulose.Usually, the other component of the catalyst system is then added andthe treated cellulosic material is brought into contact with the olefinunder proper conditions to form a shell or sleeve of the polymerdirectly on the surface of the cellulosic material. When the cellulosicmaterial is treated with the components of the catalyst system in thismanner, active catalyst sites are formed on the cellulose surfaces sothat the polymer chains grow on and from these sites as thepolymerization reaction proceeds. The use of catalyst in excess of theamount which will form active sites on the cellulosic material producesa different kind of product and should be avoided.

The cellulosic material may be treated with each of the components ofthe catalyst system in separate steps or the components may be mixedbefore treatment. However, if the components are mixed and thecellulosic material is treated in a single step, care must be exercised.If the catalyst components are mixed together for a sufficient time (forexample, 5 minutes) and then added to the cellulosic material, thepolymer that is formed is of a heterogeneous character and most or allof the polymer is in the form of separate pieces which can be readilyseparated from the cellulosic material by flotation techniques. On theother hand, if the cellulosic material is treated with any one of thecatalyst components before this component is fully reacted with theother catalyst component, the polymerization takes place at and on thesurface of the cellulosic material building up a shell of any desiredthickness on the cellulosic material.

One simple and convenient way of carrying out the treatment is by theslurry method in which the cellulosic material is suspended in asuitable liquid medium such as an organic liquid which does not dissolveor react with either cellulose or the polymer to be formed. Thecellulosic material may be treated with one of the catalyst componentsbefore or after it is placed in the suspending liquid. The othercatalyst component is then brought into contact with the cellulose, orthe two catalyst com ponents may even be added to the suspending liquidsimultaneously with the cellulosic material. The slurry of catalysttreated cellulosic material in the organic liquid, after the secondcomponent of the catalyst has been added, is treated in a closedreaction vessel with the monomer by feeding the monomer into the vesselat a suitable rate while agitating the slurry. Provisions should be madeto control the temperature of the reaction vessel, and the reactionshould be carried out under reasonably anhydrous conditions. Aspolymerization proceeds, the slurry becomes thicker and reaction isstopped at any desired stage depending upon how much of the polymer isto be formed. The slurry can then be removed from the reaction vesseland simply pressed or filtered to remove the free organic liquid andthen washed in water, methanol or other materials.

This process may be applied to a variety of different cellulosicmaterials, including not only natural cellulose such as wood, woodfibers, sawdust, wood-flour, various kinds of paper pulp, bagasse,cotton, in the form of batting, linters or filaments, line, hemp and thelike, but also regenerated cellulose such as viscose, cuprammonium orcellulose acetate rayons and cellulose compounds such as celluloseacetate and the like. For purposes of the instant invention, as will bepointed out hereinafter, it is preferred to employ natural cellulosefibers.

Catalyst systems which are useful include any two or more componentsystems which, mixed together, react to form a material that initiatesthe polymerization of the l-olefins, and which have at least onecomponent that reacts with or becomes fixed in some way on cellulosicmaterials when brought in contact therewith. In general, we have foundthat two component systems which are particularly suitable are those inwhich one component is an organometallic reagent such as an aryl of oneof the metals lithium, sodium, potassium, magnesium, calcium, zinc,cadmium, boron, or aluminum, and the other component is a transitionmetal compound such as a halide or ester of titanium, zirconium,vanadium or chronium. Other similar catalyst systems can be used as willbe apparent to those skilled in the art of producing polyolefins.

It is important, when using the catalyst systems noted above, to conductthe polymerization under substantially oxygen free and water freeconditions since the activity of the catalyst system is impaired by thepresence of any substantial amount of oxygen or water. When treatingcellulosic materials, however, more water than usual can be tolerated inthe system. A small fraction of 1% of moisture retained within thecellulose does not appear to interfere with the reaction and may in facthave a beneficial effect.

The polymerization reaction may be carried out at atmospheric pressure,or higher pressures if desired, and over a wide range of temperature.Ordinarily, the polymerization proceeds rapidly at atmospheric pressureand at a temperature between about 20 C. and about C. The amount ofpolymer formed will vary with the time of the polymerization reaction,the particular catalyst used and the particular monomer or monomersbeing polymerized. For purposes of the instant invention, the amount ofpolymer formed on the cellulose fibers should be sufiicient so that,after the cellulose fibers are removed, a self-sustaining, porous shellof polymer will remain. A polymer content of not substantially less than5% and not substantially greater than 75%, based on the total weight ofthe cellulose fibers and polymer, has been found to be acceptable. Apolymer content of not substantially less than 10% and not substantiallygreater than 50% is preferred.

The cellulose is treated, for purposes of the present invention, in theform of fibers preferably ranging from about 30 microns to 7,000 or8,000 microns in length and around 7 to 55 microns in diameter. Theindividual fibers can be substantially encased in individual shells ofthe polymer without appreciable agglomeration of the fibers. At the endof the polymerization reaction, the product is composed of fibers ofabout the original size, which are free flowing. This free-flowingproperty facilitates the molding of the polymer-encased fiber into theshape required for the finished filter. Simple heating without pressurefuses the particles together to form a porous, self-sustaining article.To increase the density and reduce the pore size, heating to fuse theparticles may be accompanied by moderate pressure. Temperatures as highas or somewhat above the crystalline melting point of the polymercoating may be employed. In the case of cellulose fibers coated withpolyethylene, a heating temperature as high as 310 F. or even higher maybe employed, while with products coated with polypropylene, otherpolyolefins or copolymers, the temperature of heating may be somewhathigher or lower depending on the crystalline melting point of thepolymer coating.

After the polymer-coated cellulose fiber is molded to the desired shapeit is subjected to a liquid, such as strong sulfuric acid solution(preferably about 70% H 50 which dissolves out the cellulose, or most ofit, leaving porous, hollow shells or tubules of the polyolefin fusedtogether in the cast or molded state. Based on microscopic and otherobservations of the manner in which the leaching out of the celluloseproceeds while leaving the shell intact, we believe that the acidpenetrates the walls of the tubules, sleeves or shells. It thereforeappears that the tubule sleeve or shell is not a completely continuousfilm, but rather possesses discontinuities through which the acid iscapable of penetrating. When the cellulose has been removed, thesediscontinuities presumably appear as pores in the walls of the remaininghollow tubes, sleeves or shells.

Thus, it is believed that two pore structures are present in the formedfilter, namely the pores formed between the fused shells or tubes andthe pores of the shell walls. This pore structure, which for purposes ofconvenience, may be referred to as a pore structure within a porestructure, is believed to account for the increased filteringeffectiveness, coupled with lowered resistance to passage of gases andvapors through the filter, that we have observed when comparing thefilters of this invention with conventional tobacco smoke filters. Thereduction of resistance to passage of gases and vapors is ofconsiderable importance in cigarette filters since it improves the drawof the cigarette.

Relatively porous cast or molded articles of substantially purepolyolefin can also be produced by dissolving out some or all of thecellulose before fusing. In this case the molding powder is composed ofa mass of hollow shells or tubes of polymer which are capable of formingcast or molded articles of varying degrees of porosity depending uponthe amount of heat and pressure applied during fusing. In this mode ofoperation, however, there is a tendency for the tubules to collapseduring the molding operation. It is, therefore, generally preferred tofirst mold the polymer-encased cellulose to a self-sustaining shapebefore extracting the cellulose. Strong sulfuric acid, caustic soda,cuprammonium solution, or other sub stances that are known to dissolveor solubilize cellulose may be used to remove cellulose from the producteither before or after molding.

The molded product is enclosed in a tube or housing having wallssubstantially impervious to air. The tube or housing is open at itsopposite ends. In use the smoke to be filtered is drawn into one end ofthe filter and is discharged from the opposite end. The tube or housingmay be formed from paper, cork sheet, or any other material imperviousto air which is suitable for the particular filter use.

In selecting a material for the housing consideration should, of course,be given to the manner in which the filter is to be used. If the end ofthe filter is to be placed in the mouth as in most filter cigarettes,the housing maerial should be, among other things, nontoxic, tastelessand resistant to moisture. Irrespective of the material employed, thehousing should envelop the molded filtering medium in such a manner thataxial air passages are not formed between the housing and the filteringmedium. Rather than forming the housing or cover from a separatematerial, the sides of the filter may be coated with a material which issubstantially air impervious or the surface may be treated to close thesurface pores for example by fusing the surface to seal the pores. Inone embodiment of the invention, the housing or cover may consist of aclosely-fitting chamber recessed in a cigarette holder, pipe stem, orthe like.

It has been found that filters produced in accordance with the instantinvention have outstanding and unusual properties as filter media. Theseproperties are no doubt at least partially attributable to the physicalstructure of the material. The microtubular form of the polymer providesa multiplicity of very fine passages, with a high proportion of voidspace. It is not difficult, under the instant invention, to form afilter having a 95% void content which has su'lficient rigidity towithstand handling and is capable of supporting reasonable loads such asthe loads normally encountered in machine production. As has been notedabove, the vast number of fine passages, coupled with the high voidcontent, provides a filter material which is highly effective and yetnot unduly resistant to the passage of gases or vapors. Also, thesurface area of the polymer in this form is so great that surfacephenomena play a significant role. As compared to conventional filtermaterial made of cellulose fibers, the material according to the presentinvention is composed of fiber-shaped, tubules, each of which isapproximately of the dimensions of a cellulose fiber but, instead ofbeing solid, is a hollow tube having porous walls. This configurationincreases the surface area and void space enormously as compared tofilters made of bundled cellulose fibers. Thus, adsorption takes placeto a very considerable extent, where impurities in the material to befiltered are of such a nature as to be adsorbable on an olefin polymersurface. The porous walled tubules form numerous traps for materials tobe removed. The filter of the instant invention is impervious to water.However,

while impervious to water, it is not impervious to Water vapor. Thus,the water vapor content of the cigarette smoke is not substantiallyreduced in passing through the filter. This is of considerable advantagesince it permits the filter to be used without making the smoke dry andharsh.

The inertness of the polyolefin materials to water leads to stillanother important advantage. When a conventional cellulosic filterbecomes moistened by contact with saliva, as occasionally happens, themoistened fibers swell, impeding the passage of smoke through the filterand causing the cigarette to draw with difiiculty. In addition to makingsmoking more difficult, when the draw is increased channels tend to formthrough the filter which reduce the filters eifectiveness. The filter ofthe present invention neither wets nor swells, and difficulties of thisnature are not encountered.

In order to illustrate more fully the nature of this invention and themanner of practicing the same, the following example is presented.

Example A polyethylene-encapsulated cellulose composition was preparedas follows:

Twenty-four grams of wood cellulose floc were dispersed in 1400 cc. oftoluene under dry conditions. The air in the vessel was replaced withnitrogen and 0.3016 mol of TiCl were added to the dispersion. Thismixture was allowed to react one-half hour at room temperature to bringabout the titanation of the cellulose, after which 0.075 mol ofmethylmagnesium bromide were added. The temperature was raised to andmaintained at 5060 C., while a stream of gaseous ethylene was passedthrough the mixture. The color changed from orange through dark green toalmost black. The how of ethylene was continued for six hours, until therate of absorption became negligible. The amount of ethylene absorbedwas approximately equal to the amount of cellulose has in the reactionvessel.

The solution was cooled and diluted by adding an equal volume ofmethanol, and the cooled solution was filtered and washed withadditional methanol. The filter cake, after drying, was a white, powderycellulose-polyethylene composition containing approximately 50%polyethylene.

This composition was fabricated into a rod by heat-fusing in a glassmold. A glass tubing approximately six inches long was closed at one endand filled with the cellulose-polyethylene composition, with lighttam-ping. The glass tube was then immersed for three minutes in an oilbath maintained at C., and then withdrawn and cooled. The fused rod ofcellulose-polethylene composition thus formed shrank slightly in thefusing, and could easily be removed from the tube. A tube of 89 mm.inside diameter was found to give a sintered rod of approximately theproper diameter for use as a cigarette filter. The rod was then treatedtwice with 70% sulfuric acid to extract the cellulose and washedrepeatedly with water to remove the acid. The rod at this stageconsisted of a mass of hollow, porous tubules of polyethylene, sintercdtogether at the points where they touched. After drying, the rod was cutinto lengths corresponding to the length of a typical commercialcigarette filter (17 mm).

The etlicacy of the filters so produced was tested by substituting suchfilters for the original filters in commercial filter cigarettes andrunning comparative smoking tests. The smoking apparatus was made fromglass tub ing and protected from air drafts by a glass funnel clippedover the cigarette receiver, which was a short piece of glass tubing.The receiver was connected with rubber tubing to a glass stopcock andthence to an aspirator flask. The test was carried out by inserting acigarette in the receiver, lighting it, and allowing it to burn downclose to the holder, the necessary suction being provided by theaspirator, which was kept running at a constant rate. When the cigarettewas consumed, the aspirator was turned off, the cigarette butt wasremoved from the receiver and the filter was removed from the butt. Thefilter was then dropped into a test tube containing ml. of benzene andthe test tube was stoppered.

After twenty-four hours extraction in the test tube, during which thetube was shaken several times to speed extraction of tars, the solutionwas shaken again to ensure thorough mixing and the color intensity ofthe solution was measured with a spectrophotometer at various wavelengths.

The entire procedure was carried out repeatedly, and the color intensity(indicated by greater light absorption) was invariably about higher inextracts of the filters of this invention, as opposed to those of thecommercial filters. This indicates a substantial improvement in theefiiciency of the filters of this invention over commercial filters inthe removal of tars from the smoke stream. it was also noted that afterextraction as described, the commercial filters were almost white, whilethe originally white filter according to this invention remaineddistinctly brown, indicating the stubborn retention by the filteraccording to the invention of additional amounts of tar over and abovethat removed by the solution. Seven commercial brands of filtercigarettes were compared with the filters according to this invention,with substantially the same results in all cases; the filter accordingto this invention trapped about 25% more tars as indicated by solutioncolor intensity, plus a further increment of indeterminate magnitude,indicated by the residual color in the extracted filter. Organoleptictests of the filters of the instant invention revealed that the smokingqualities of the cigarettes made with filters of this invention were, ingeneral, as good as those of commercial cigarettes, and frequentlybetter.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible Within the scope of theinvention claimed.

What is claimed is:

1. A filter suitable for filtering tobacco smoke comprising a mass ofhollow tubules of a polymer of a monomer selected from the groupconsisting of aliphatic 1-olefins having less than 6 carbon atoms, saidtubules being randomly oriented and in contact and forming intermediatetheir points of contact, tortuous paths for the passage of smoke throughsaid mass, said hollow tubules having porous walls, the pores in saidwalls connecting the interiors of said tubules with said tortuous paths,and a casing open at its opposite ends surrounding said mass, saidcasing intermediate said opposite ends being substantially impervious toair.

2. A filter suitable for filtering tobacco smoke comprising aself-supporting mass of hollow tubules of a polymer of a monomerselected from the group consisting of aliphatic l-olefins having lessthan 6 carbon atoms, said tubules being randomly oriented and fusedtogether at their points of contact to form intermediate said points ofcontact a pore structure through said mass, said hollow tubules havingporous walls, the pores in said walls connecting the interiors of saidtubules with said pore structure and a casing open at its opposite endssurrounding said mass, said casing intermediate said opposite ends beingsubstantially impervious to air.

3. A filter as recited in claim 2 in which said monomer is ethylene.

4. A filter as recited in claim 2 in which said monomer is propylene.

5. A filter as recited in claim 2, wherein said casing consistsessentially of an open-ended tube of impervious sheet materialenveloping said mass of tubules.

6. A filter as recited in claim 2, wherein said casing consistsessentially of an outer layer of pore-sealing material on the sides ofsaid filter.

'7. A filter as recited in claim 2, wherein said casing consistsessentially of a surface area of said mass of tubules, said surface areabeing fused to seal the pores thereof.

8. A filter as recited in claim 2, wherein said casing consistsessentially of a hollow, nonporous tube adapted to fit snugly aroundsaid mass of hollow, porous tubules.

9. A filter tip cigarette comprising a housing open at its oppositeends, tobacco in one end of said housing and a filter in the oppositeend of said housing, said filter comprising a mass of hollow tubules ofa polymer, said tubules being randomly oriented and joined together attheir points of contact to form, intermediate said points of contact,tortuous paths for the passage of smoke through said mass axially ofsaid housing, said hollow tubules having porous walls, the pores in saidwalls connecting the interiors of said tubules with said tortuous paths,said housing adjacent said compacted mass being substantially imperviousto air.

10. A filter tip cigarette as recited in claim 9 in which said polymeris a polymer of a monomer selected from the group consisting ofaliphatic l-olefins having less than 6 carbon atoms.

11. A filter tip cigarette as recited in claim 10 in which said monomeris ethylene.

12. A filter tip cigarette as recited in claim 10 in which said monomeris propylene.

13. A filter for use with a filter casing having open ends and wallsthat are substantially impervious to air, said filter comprising a massof hollow tubules of a polymer, said tubules being randomly oriented andjoined together at their points of contact to form, intermediate saidpoints of contact, tortuous paths for the passage of smoke through saidmass axially of said casing, said hollow tubules having porous walls,the pores in said walls connecting the interiors of said tubules withsaid tortuous paths.

References Cited by the Examiner UNITED STATES PATENTS 1,631,071 5/1927Smelling 264166 2,763,267 9/1956 Muller 13110 2,765,515 10/1956 Knudson131-208 2,854,985 10/1958 Watkins 131l0 2,916,038 12/1959 \Vade 131102,966,157 12/1960 Touey et a1. 131208 3,025,130 3/1962 White l31208FOREIGN PATENTS 121,414 3/ 1944 Australia. 590,629 4/1959 Italy.

SAMUEL KOREN, Primary Examiner. MELVIN D. REIN, ABRAHAM G. STONE,Examiners.

9. A FILTER TIP CIGARETTE COMPRISING A HOUSING OPEN AT ITS OPPOSITEENDS, TOBACCO IN ONE END OF SAID HOUSING AND A FILTER IN THE OPPOSITEEND OF SAID HOUSING, SAID FILTER COMPRISING A MASS OF HOLLOW TUBULES OFA POLYMER, SAID TUBULES BEING RANDOMLY ORIENTED AND JOINED TOGETHER ATTHEIR POINTS OF CONTACT TO FORM, INTERMEDIATE SAID POINTS OF CONTACT,TORTUOUS PATHS FOR THE PASSAGE OF SMOKE THROUGH SAID MASS AXIALLY OFSAID HOUSING, SAID HOLLOW TUBULES HAVING POROUS WALLS, THE PORES IN SAIDWALLS CONNECTING THE INTERIORS OF SAID TUBULES WITH SAID TORTUOUS PATHS,SAID HOUSING ADJACENT SAID COMPACTED MASS BEING SUBSTANTIALLY IMPERVIOUSTO AIR.